Not limited to, but particularly in the case where an electromagnetic beam is utilized to investigate a sample system which presents with a varying depth surface topology, it is important to provide an electromagnetic beam of a known lateral dimension and which presents with a relatively simple cross-sectional Intensity profile.
It is noted that often electromagnetic beams present with a substantially arbitrary intensity profile, with the highest intensity generally being located centrally, and with intensity decreasing with increasing radius. While such a beam intensity profile is typically acceptable for use in ellipsometry and related practices, it has been found that once the intensity of a substantially arbitrary profile beam of electromagnetic radiation has dropped to, as an arbitrary example, say ten (10%) of its maximum, that said intensity in many beams does not always continue to decay directly to essentially zero (0.0). Instead, it often presents irregularly as a function of radius, (eg. easily visualized as being generally similar to the Fourier transform of a square wave). The cause of said irregular intensity profile can include such as optical element wavelength dependent diffraction, surface roughness or other non-idealities, and where, for instance, electromagnetic radiation is provided via an aperture or via the end of a light fiber contained in a cladding, such that electromagnetic radiation falls outside a geometric image thereof.
It would be of benefit, as regards obtaining accurate data from application of ellipsometers and the like systems, if the intensity of an electromagnetic beam could be forced to decay quickly to zero (0.0), rather than demonstrate an irregular intensity profile as a function of radius.
With an eye to the present invention, a Search of Patents was conducted. With respect to the Spatial Filter aspect of the Disclosed Invention, perhaps the most relevant Patent identified is No. 5,517,312 to Finarov. Said 312 Patent describes application of a scattered light reducing system at the entry to a Detector of an Ellipsometer or Spectrophotometer System, which scattered light reducing system consists of two lenses with a pin-hole containing diaphram located midway therebetween, and at the focal lengths of said lenses. Said scattered light reducing system is present after a sample system and processes electromagnetic radiation after it interacts with said sample system. The pinhole is described as serving to provide high spatial resolution as well as reduce scattered light. Another Patent identified is that to Campbell et al., U.S. Pat. No. 5,148,323. Said 323 Patent describes a Spatial Filter in which a pinhole is located other than at the focal length of a converging lens. U.S. Pat. No. 3,905,675 to McCraken describes a Spatial Filter containing system which enables observation of a weak source of electromagnetic radiation in the presence of strong sources thereof. U.S. Pat. No. 5,684,642 to Zumoto et al., describes an optical transmission system for use in fashioning an electromagnetic beam for use in machining materials which combines a Spatial Filter and an Optical Fiber. U.S. Pat. No. 4,877,960 is identified as it describes masking energy from outside the target area of a in a microscope having dual remote image masking. U.S. Pat. No. 5,426,506 to Ellingson et al. is disclosed as it teaches a Spatial Filter after a reflecting means in an optical apparatus for detection of surface defects in dense ceramics. (Note that the disclosed inventions either has no reflecting means for directing an electromagnetic beam, or places a spatial filter before, not after, a reflecting means. U.S. Pat. No. 6,134,012 to Aspnes; U.S. Pat. No. 6,321,601 to Maris; and U.S. Pat. No. 4,996,120 to Smothers et al. are disclosed as they are known to the Applicant.
With respect to the Beam Energy Homogenization aspect of the Disclosed Invention, Patents disclosed are U.S. Pat. No. 5,608,526 to Piwonka-Corle et al. which describes application of optical elements with other than radial symetry in ellipsometer systems, however, typical application thereof is to enter compensation for various aberational effects. U.S. Pat. No. 5,859,424 to Norton et al. discloses use of an apodizing filter used to reduce spot size in optical measurements. Patent to Burghardt et al., U.S. Pat. No. 5,414,559 is disclosed as it describes a device for homogenizing a light beam. U.S. Pat. No. 5,796,521 to Kahlert et al. is disclosed as it describes optical apparatus for homogenizing electromagnetic beams which comprises cylindrical lenses.
Even in view of the known art, especially in the context of polarimeter, ellipsometer, reflectometer, spectrophotometer and the like systems, a need exists for a means to fashion a beam with a radially arbitrary intensity profile that does not quickly decay to zero, into a beam in which the energy intensity is relatively homogeneous radially and approaches zero intensity quickly beyond its extent.